From 09ccf5549d7809671af34774bb30c8f935d6ed2b Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Fri, 10 Jan 2025 08:37:34 +0100 Subject: [PATCH] loop: only write back pagecache when starting to to use direct I/O There is no point in doing an fdatasync to write out pages when switching away from direct I/O, as there won't be any. The writeback is only needed when switching to direct I/O, which would have to invalidate the pagecache less efficiently from the I/O path. Signed-off-by: Christoph Hellwig Link: https://lore.kernel.org/r/20250110073750.1582447-5-hch@lst.de Signed-off-by: Jens Axboe --- drivers/block/loop.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 55bea9c95b45..cf80cdf5e440 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -203,8 +203,9 @@ static void __loop_update_dio(struct loop_device *lo, bool dio) if (lo->use_dio == use_dio) return; - /* flush dirty pages before changing direct IO */ - vfs_fsync(lo->lo_backing_file, 0); + /* flush dirty pages before starting to use direct I/O */ + if (use_dio) + vfs_fsync(lo->lo_backing_file, 0); /* * The flag of LO_FLAGS_DIRECT_IO is handled similarly with -- 2.50.1